Loud-speaker circuits



w. MARTIN LOUD SPEAKER CIRCUITS Filed Jun 1'7, 1922 INVENTOR. W17:Miriam ATTORNEY time nee le, 1924. v 3

UNITED STATES PATENT OFFICE.

H. MARTIN, OF NEW YORK-, N. Y., ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

LOUD-SPEAKER CIRCUITS.

Application flledJune 17, 1922. Serial No. 568,847.-

k To all whom it may concern:

Be it known that I, WILLIAM H. MARTIN, residing at New York, in thecounty of Bronx and State of New York, have invented certainImprovements in! Loud- Speaker Circuits, of which the following is aspecification. V

This invention relates to improvements in telephone circuits andparticularly to the types of circuits suitable for use with loud speakerapparatus.

The field of use for the loud speaking telephone is found to extend,among other things, to announcing systems, phonograplh reproduction,intercommunication, and

giving of public address or other performance. It often happens that incircuits designed for the above purposes, and particularly for theurposes of public address or announcing, t at the loud speaking receiverwill be located in relatively close proximity to the transmitter and asa result an acoustic coupling may exist between the receiver andtransmitter, which may impress sufficient energy upon the transmitter tocause singing to take place in'the circuit. In general it is the objectof this invention to prevent such singing in loud speaker circuits byroviding an additional electric coupling etween receiver and transmitterwhich is adjusted to neutralize theetlect of any acoustic coupling whichmay exist between them. Other features of the invention will appear morefully from the detailed description hereinafter given.

' The invention ma be more fully understood from the fol owingdescription together'with the accompanying drawing in the figure ofWhich is illustrated a circuit diagram of a loud speaker systemembodying the invention.

In the drawmg is shown a transmitter T. The condenser type oftransmitter, or any 7 other desired type, may be used. The

transmitter T is included in a transmitter circuit 1 which includes abattery, a winding of. transformer 1, and a series resistance 1' Theother winding of transformer 2 is connected to an amplifier circuit,which includes the vacuum tube amplifier A The output of the amplifieris connected through a transformer 3 to a receiver circuit 4, whichincludes the series resistance r, and the loud speakin receiver .R whichis illustrated schematically as it is of a well known type.

If, as often may be the case, the receiver R is su'fiiciently close tothe transmitter T,

it may cause the voice waves to be impressed through the air upon thetransnntter T and thus cause singing to take place in the circuit. Inother words the acoustic coupling) between the receiver and transmittermay e suiliciently great so that, when operating through theamplification in the electrical circuit between the transmitter and thereceiver, a flow of energy is I A is connected to a distortion networkN. I

The distortion network N is connected to circuit 6 which is bridgedacross the terminals of resistance r, in the transmitter cireuit 'l. Thedistortion network N comprises a series and shunt combination ofresistance, inductance and capacity, the elements of, which may bevaried. With this arrangement the original energy from the transmi tterwill be transmitted through the ampliiier A, to the receiver circuit 4:and will actuate the loud speaker R. A. portion-of the sound from ,theloud speaker B may affect the transmitter T and tend to cause acirculation of energy, or singing. However, at the same time a portionof the energy from the receiver circuit will be transmitted over circuit5, 7 through amplifier A and distortion network N, and over circuit (3to the transmitter circuit 1. This energy can be made to neutralize theeffect of the energy transmitted acoustically and will prevent singingfrom taking place. The amplifier A and distortion network N obviouslymust be adjusted differently to meet diil'erent acoustic conditions. Thedistortion network N needs to be adjusted for both variation ofeiiiciency with frequency and phase relation with frequency.

While the arrangements of the invention have been disclosed as embodiedin certain s ecific arrangements which are deemed deslrable, they arecapable of embodiment in lilil man other types of circuit arrangementswithout departing from the spirit of the invention as defined by theappended claims.

What is claimed is: 1. circuit including a transmitter and a receiver soarranged that an acoustic coupling exists between said receiver andtransnntter, and an electric coupling asso- 'ciated with sa d circuitadapted to neutralize the effect of said coupling, said electriccoupling comprising an amplifier and a distortion network and means foradjusting the same.

2. A loud speaker system comprising a transmitter circuit and a receivercircuit, an.

amplifier circuit interconnecting said eiruits, a series resistance insaid receiver circuit, a'series resistance in said transmitter circuit,an input circuit associated by a variable connection with first saidmentioned resistance, an amplifier in said input circuit, a variabledistortion network associated with the output of said amplifier, and acircuit connecting said distortion network to said second mentionedresistance;

3. A circuit including a transmitter and a. receiver so arranged that anacoustic coupling exists between said receiver and transmitter, anelectric coupling associated .June, 1922.

WILLIAM H. MARTIN.

